Heretofore, a piezoelectric speaker has been known as a miniature low-current driven sound device having a piezoelectric material used as an electric acoustic transducer element. The piezoelectric speaker has been used as a sound output device of a miniature electronic apparatus (see, for example, patent literature 1). In general, a piezoelectric speaker has a structure in which a piezoelectric element, formed with an electrode of a thin silver film or the like, is attached to a metallic diaphragm. The piezoelectric speaker generates a sound in such a manner that an alternate current voltage is applied across both faces of the piezoelectric element so as to generate shape distortion on the piezoelectric element so that the metallic diaphragm to which the piezoelectric element is attached and integrated is vibrated.
The piezoelectric speaker disclosed in the patent literature 1 includes a frame, a diaphragm, a piezoelectric element provided on the diaphragm, a damper that is connected to the frame and the diaphragm and supports the diaphragm so as to allow the diaphragm to linearly vibrate, and an edge formed so as to plug an air gap among the diaphragm, the damper and the frame. The diaphragm, the damper and the edge are formed on an identical plane. The word of “linearly” means that the entire face of the diaphragm vibrates in a roughly parallel state in contrast with a drum-like action. Accordingly, an amplitude volume is increased so that reproduction of a low frequency band can be made easy.
On the other hand, a structure in which a function of a piezoelectric speaker is integrated with a function of an antenna is provided (see, for example, patent literatures 2 and 3). A selective call device disclosed in the patent literature 2 includes a wireless reception section, a piezoelectric speaker for generating an alarm sound, and an alarm sound generation section. An input terminal of the wireless reception section and a metallic base section are connected to form an antenna.
In addition, an antenna integrated with a speaker disclosed in the patent literature 3 includes a plate-like first antenna element to which a piezoelectric material is attached, a plate-like second antenna element provided away from the first antenna element at a predetermined distance, and a connection wire electrically connecting the first and second antenna elements to each other. The first and second antenna elements vibrate when a sound signal is applied to the piezoelectric material.    Patent Literature 1: JP-UM-A-1-115347    Patent Literature 2: JP-A-2001-016692 (Japanese Patent No. 3160271)    Patent Literature 3: JP-A-2006-186881